The present invention relates to a flow rate control valve and/or a fuel vapor processing apparatus including the flow rate control valve.
Conventionally, there exists fuel vapor processing apparatuses including: a canister that may adsorb and desorb vapor generated in the fuel tank of a vehicle on that an internal combustion engine is mounted; a vapor passage connecting the fuel tank and the canister; a purge passage connecting the canister and an intake passage of the internal combustion engine; a purge valve capable of opening and closing the purge passage; a closing valve capable of opening and closing the vapor passage; and a controller configured to control the purge valve and the closing valve (See, for example, Japanese Laid-Open Patent Publication No. 2000-73883). In Japanese Laid-Open Patent Publication No. 2000-73883, the closing valve (to which the “bypass valve” of Japanese Laid-Open Patent Publication No. 2000-73883 corresponds) is driven to be opened and closed by a stepping motor. A general flow rate control valve driven to be opened and closed by a stepping motor includes a valve casing configured to form a fluid passage, a valve seat installed in the fluid passage of the valve casing, an electric motor installed in the valve casing and configured to be drive-controlled by the controller, a valve body axially stroke-controlled via a feed screw mechanism by the electric motor to be placed and separated on and from the valve seat, and a spring for biasing the valve body in a closing direction.
When the flow rate control valve is in a valve-closed state, electricity supply to the stepping motor is stopped while the valve body is seated on the valve seat. As a result, the valve seat of the valve casing, the stepping motor and the feed screw mechanism may regulate the movement of the valve body in the axial direction. In this state, a change in dimension in the valve casing, in particular, a change in dimension in the axial direction of the valve body may be generated due to a change in temperature. When, for example, the valve casing expands in the axial direction of the valve body, the distance between the stepping motor and the valve seat increases, and the sealing force between the valve body and the valve seat is reduced. When the valve casing is reduced in the axial direction of the valve body, the distance between the stepping motor and the valve seat is reduced. At this time, the valve body gets cramped up, so that there is a fear of defective operation.
To eliminate the above problem, it might be possible to set the lead angle of the feed screw mechanism large to thereby increase the spring force of the spring. Then, in the so-called non-electricity-supply state in which the electricity supply to the stepping motor is stopped, the motor side member of the feed screw mechanism would be rotated as the valve body is pressed against the valve seat. This may maintain the valve body to be seated on the valve seat to solve the above problem. That, however, involves the following problems: (1) a stepping motor of large thrust is required, resulting in an increase in size and cost; (2) also when keeping the valve body at rest in the open state at the time of fuel supply, depressurization control, etc., electricity supply is required, resulting in involvement of power consumption; and (3) the stroke amount of the valve body per 1 step of the stepping motor (the stroke resolution) increases, resulting in deterioration in flow rate control property.
It is an object of the present invention to provide a flow rate control valve capable of avoiding the problem due to a change in the dimension of the valve casing in the closed state, and a fuel vapor processing apparatus including the flow rate control valve.